Carbazolyl-stabilised phosphaketenyltetrylenes were prepared and photolytically decarbonylated. The germylene and stannylene derivatives afforded diphosphene-type dimers, while the plumbylene displayed an unexpected isomerisation reaction and incomplete decarbonylation.

Abstract

Phosphaketenes of divalent group 14 compounds can potentially serve as precursors for the synthesis of heavy multiple-bond systems. We have employed the ^dtbpCbz substituent (^dtbpCbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl) to prepare such phosphaketenyltetrylenes [(^dtbpCbz)EPCO] (E=Ge, Sn, Pb). While the phosphaketenyltetrylenes are stable at ambient conditions, they can be readily decarbonylated photolytically. For the germylene and stannylene derivatives, dimeric diphosphene-type products [(^dtbpCbz)EP]₂ (E=Ge, Sn) were obtained. In contrast, photolysis of the phosphaketenylplumbylene, via isomerisation of the [(^dtbpCbz)PbP] intermediate to [(^dtbpCbz)PPb], afforded an unsymmetric and incompletely decarbonylated product [(^dtbpCbz)₂Pb₂P₂CO] formally comprising a [(^dtbpCbz)PPb] and a [(^dtbpCbz)PbPCO] moiety.